Splenic vein thrombosis (SVT) can lead to gastric varices through a process involving localized portal hypertension in the splenic venous system. Here’s a clear explanation of the mechanism:

1.  Splenic Vein Obstruction:

•  SVT occurs when a blood clot blocks the splenic vein, which drains blood from the spleen and parts of the stomach (e.g., short gastric and left gastric veins).

•  Common causes include pancreatitis, pancreatic cancer, trauma, or hypercoagulable states.

2.  Increased Pressure in Collateral Veins:

•  The thrombosis prevents normal blood flow from the spleen and stomach to the portal vein.

•  Blood seeks alternative routes, leading to increased pressure in the short gastric veins and left gastric veins, which are tributaries of the splenic vein.

3.  Formation of Gastric Varices:

•  The elevated pressure causes dilation of these collateral veins, particularly in the fundus of the stomach, forming gastric varices.

•  Unlike esophageal varices (more common in generalized portal hypertension from liver cirrhosis), gastric varices from SVT are often isolated and termed sinistral or left-sided portal hypertension.

4.  Why the Stomach?:

•  The stomach’s venous drainage (via short gastric and left gastric veins) is directly affected by splenic vein obstruction.

•  These veins hypertrophy to bypass the blockage, creating varices in the gastric wall, especially in the submucosa of the fundus.

5.  Key Features:

•  Gastric varices from SVT typically occur without widespread portal hypertension or liver dysfunction, distinguishing them from varices caused by cirrhosis (e.g., in PSC or PBC).

•  The spleen may enlarge (splenomegaly) due to venous congestion, but liver function tests are usually normal unless another condition is present.

6.  Clinical Relevance:

•  Gastric varices can bleed, presenting as upper GI bleeding (hematemesis, melena).

•  Diagnosis involves imaging (e.g., CT/MRI showing SVT and varices) and endoscopy (visualizing fundal varices).

•  Treatment may include splenectomy (to eliminate the collateral flow), anticoagulation (for reversible causes), or endoscopic interventions (e.g., cyanoacrylate injection) for bleeding.